U.S. Pat. No. 2,480,980 to Terhaar recognizes that blood circulation can be influenced by general pressure changes around the chest. U.S. Pat. No. 3,078,842 to Gray has proposed a method and apparatus for applying alternating pressures to the thorax at the respiratory rate, and superimposing thereon sharp pressure bursts or pulses at the cardiac pulse rate, to promote or effectuate blood circulation.
A considerable body of pertinent information has been summarized in two recent articles, viz., Fenster, P. E. and Ewy, G. A., "Cardiopulmonary Resuscitation: Recent Insights and New Developments," Practical Cardiology, Vol. 6, No. 5, May 1, 1980 pp. 15-19, and Chandra, N., Rudikoff M. and Weisfeldt, M. L., "Simultaneous Chest Compression and Ventilation at High Airway Pressure During Cardiopulmonary Resuscitation," The Lancet, Jan. 26, 1980, pp. 175-178. While these two articles do not necessarily antedate the present invention, the articles and their respective bibliographies are incorporated by reference herein to provide background and theoretical information.
Conventional cardiopulmonary resuscitation (CPR) dates back to the efforts of Jude and Kouwenhoven who in 1959, described maintaining effective circulation with precordial compression. It was popularly thought at that time and the idea was promulgated and accepted, that the motive force was the result of compression of the left ventricle between the sternum and the vertebral column.
Considerable evidence is now available to suggest that the real mechanism of circulation is the effect of the abrupt increase in intrathoracic pressure on the aorta and great vessels. This compression of the elastic aorta, in the presence of a competent aortic valve propels the blood into capillary circulation in a "forward" fashion.
The first piece of evidence relates to the well-known effect of repetitive coughing which is utilized in most cardiac catheterization laboratories in response to prolonged bradycardia, or cardiac arrest. Patients are commonly instructed prior to catheterization to cough sharply and repeatedly upon command. The effect of this coughing is readily apparent since these patients commonly are under circumstances of physiologic recording of intra-arterial pressure. Commonly such coughing produces systolic blood pressures over 100 mm. of mercury, and this critical perfusion technique can be continued even in the face of ventricular fibrillation or asystole. The mechanism here includes utilization of the voluntary muscles of coughing, including intercostals, abdominal muscles and diaphragms (the effect on the abdominal aorta may also have to be considered in light of the abdominal compression methods that have been used to add to the efficience of cardiac massage. These have been reported in the last year.)
The second item of evidence relates to recent Doppler flow studies which reveal that, with standard CPR techniques, aortic flow begins before the opening of the aortic valve. This also indicates a noncardiogenic flow phenomenon.
Since the turn of the century, there have been many proposals for machines to assist or to automatically effectuate respiration by external compression of the thoracic and/or abdominal regions. U.S. Pat. No. 651,962 to Boghean has proposed a respirator comprising a plurality of rigid plates shaped to engage the thorax and mounting rollers on the outside for guiding a cord that is automatically tautened and loosened periodically by the action of a pull roller operated by a cam and motor arrangement. Other examples of respirators using bands or straps are described in the U.S. Pat. Nos. 2,071,215 Petersen, 2,486,667 Meister, 3,777,744 Fryfogle and 4,004,579 Dedo. Straps or bands may be combined with manually operated or power driven pad and plunger arrangements that exert localized pressure on the sternum in a manner that simulates manual CPR methods of maintaining blood circulation, for example, as described in the U.S. Pat. Nos. 3,425,409 Isaacson and 4,060,079 Reinhold.
To be effective, both manual CPR methods and mechanically implemented or assisted methods that depend mainly on the application of pressure to the sternum often require the use of force sufficient to produce incipient damage to the body structures of the patient. Many otherwise qualified persons have been physically incapable of performing effective manual CPR because they lack sufficient strenth, body weight, or agility. On the other hand, the use of excessive or misdirected force can result in severe injury to the patient. If a sufficient and adequately abrupt increase in the intrathoracic pressures can be generated by the application of forces properly distributed over wider areas of the thoracic periphery, the probability and extent of injuries should be substantially reduced.
There have been many proposals for resuscitation jackets or cuirass units whereby pneumatic pressure variations could be used to apply evenly distributed forces to the thoracic regions. These units or jackets were designed basically to produce artificial respiration or to assist natural breathing. The Terhaar and Gray patents supra contain what are essentially proposals to adapt the then-existing respirator designs so that they could be used to resuscitate patients suffering from cardiocirculatory arrest. These designs, like those proposing compression devices using cords, bands or straps for distributing pressures around the thorax as in the Boghean, Petersen, Meister, Fryfogle and Dedo patents supra do not seem well adapted for cardiocirculatory resuscitation.
The situation of a patient undergoing cardiocirculatory arrest is much more critical in many respects, than that of one merely requiring respiratory aid. The time problem is especially acute, since the patient can suffer brain damage around four minutes after the heart stops, and if circulation is not restored before six minutes have elapsed, brain damage is almost certain to occur. Frequently some or most of this critical time will already have elapsed before the situation of the patient is discovered and the cardiac arrest is confirmed. Cardiocirculatory resuscitation requires considerably greater thoracic compression forces than those necessary for respiratory resuscitation. The cardiocirculatory resuscitation forces need to be applied and released more abruptly, at a much higher alternation frequency, and with the exercise of a greater measure of control. Frequently the resuscitative application of the rhythmic thoracic compressions needs to be carried out without interruption simultaneously with the use of fluoroscopy as an aid to examination and/or to the placement of catheters in or near the heart.
Accordingly there is at present a need for improved methods and apparatus for resuscitating a patient having cardiocirculatory arrest; which methods and apparatus can be routinely placed in operation in less than about ten seconds after the patient is in position; which adjust in a semiautomatic or automatic manner to patients of disparate body shapes and sizes; which readily permit the application of adjustable, reproducibly measured and continually monitored pressures and thoracic compression distances as specified by the physician or other person in charge; which can apply such pressures that are either uniform around the major portion of the thorax or locally intensified at a selected portion thereof such as over the sternum; which minimize the probability of inflicting bodily structural damage or skin irritation on the patient; which can be converted in a few seconds from a manual mode of operation to a power driven, automatic cycling mode and vice versa; which in the manual mode provide a mechanical advantage to ease the effort of the operator and are operable with a natural body movement from an adjustable and relatively comfortable body position; which keep the front and rear areas of the thorax clear and free of any activity or appurtenances that can interfere with the use of a fluoroscope for placing heart catheters while CPR is in progress, and which can include a base or support that will serve as a litter for handling and transporting a patient, even allowing effective CPR activity to be continued while the patient is in transit.